Gamma-Ray Lines in 15 Years of Fermi-LAT Data: New Constraints on Higgs Portal Dark Matter

Abstract

Monoenergetic ${\hat{I}}^3$-ray spectral lines are among the cleanest signatures of dark matter annihilation. We analyze 15 years of Fermi-LAT data, find no spectral lines, and place strong constraints on dark matter annihilation to monoenergetic ${\hat{I}}^3$-rays. Additionally, we produce the first double-line analysis of the coupled signals from ${\hat{I}}^3{\hat{I}}^3$ and $Z{\hat{I}}^3$ lines, which proves particularly powerful for dark matter masses above $\sim 150$~GeV. From our constraints on a double-line feature, we investigate and constrain some minimal models where the Galactic Center Excess (GCE) can be fit by dark matter annihilation through the Higgs boson into Standard Model particles.

12 pages, 9 figures